The present invention generally relates to an environmental control system, and more particularly, to an augmented catalytic heat exchanger system and method for removing one or more pollutants from an air stream.
Commercial aircraft feed bleed air from a gas turbine engine to an environmental control system (ECS) and thence to an interior air space, e.g., cabin or flight deck of the aircraft. The ECS conditions the air it receives in terms of pressure, temperature, and humidity to provide for the comfort of flight crew and passengers.
Modern jet (gas turbine engine) aircraft are typically designed for fuel-efficient operation at relatively high altitudes of 25,000 feet or more where the atmospheric ozone content is relatively high. The ozone concentration may depend on a number of factors, such as the altitude, geographic location, time of year, etc. The ozone concentration in the atmosphere is typically in the range of from about 0.2 to 2.0 ppm. The upper limit permitted by FAA regulations for the ozone concentration in cabin air of commercial aircraft is 0.1 ppm. Excessive levels of ozone can cause a number of medical problems, including lung and eye irritation, headaches, fatigue, and breathing discomfort.
In the prior art, vehicular environmental control systems have used a catalytic converter for the removal of ozone, wherein the catalytic converter is a stand-alone device, thereby adding weight to the ECS. Adding weight to the ECS may be a major disadvantage, particularly in the case of aircraft. A stand-alone catalytic converter may also cause an undesirable pressure drop across the system. Furthermore, due to the relatively low surface area of conventional catalytic converters, the maintenance period is relatively short, and direct maintenance costs are consequently relatively high.
U.S. Pat. No. 5,151,022 to Emerson et al. discloses an ECS for a vehicle for removing nuclear, biological, and chemical warfare agents from air, wherein the ECS includes a primary heat exchanger and a catalytic converter as a separate device.
U.S. Pat. No. 4,665,973 to Limberg et al., discloses an ECS including a catalytic heat exchanger for the removal of ozone. However, Limberg et al. does not disclose an ancillary or augmentative catalytic device to be used in conjunction with the catalytic heat exchanger. Consequently, due to the relatively low catalytic conversion efficiency, for example about 60%, of a stand-alone catalytic heat exchanger, the ECS of Limberg et al. may fail to meet FAA regulations on ozone concentration in cabin air, or may require frequent maintenance to boost the catalytic conversion efficiency to a point sufficient to meet such FAA regulations.
FIG. 1A schematically represents, in side view, a portion of an ECS 10 for a vehicle (not shown), including a primary heat exchanger 12 and a stand-alone catalytic converter 14, according to the prior art. An air stream 18 may be passed through primary heat exchanger 12, which cools the air but does not remove ozone from air stream 18, and thence, via a conduit 16, to catalytic converter 14, which removes one or more pollutants from air stream 18. In the case of a commercial aircraft, primary heat exchanger 12 and catalytic converter 14 may have a weight of about 44 Kg and 5.8 Kg, respectively.
FIG. 1B schematically represents, in side view, a portion of an ECS 10′ for a vehicle (not shown), including a stand-alone catalytic primary heat exchanger 12′, also according to the prior art. An air stream 18 may be passed through catalytic primary heat exchanger 12,′ which both cools the air and catalytically removes one or more pollutants.
A disadvantage with the prior art system of FIG. 1A is that the combined weight of primary heat exchanger 12 and catalytic converter 14 greatly exceed that of a catalytic heat exchanger (e.g., catalytic heat exchanger 12′ of FIG. 1B). A further disadvantage with the prior art system of FIG. 1A is that the catalytic efficiency, e.g., the ozone conversion efficiency, may decrease over a relatively short operation period, such that extensive maintenance of catalytic converter 14 is required within a period of from about 9,000 to 22,000 hours.
A disadvantage of catalytic heat exchanger 12′ of FIG. 1B is that the catalytic efficiency, e.g., the ozone conversion efficiency, may be considerably less that that of the prior art system of FIG. 1A.
As can be seen, there is a need for an ECS including a catalytic primary heat exchanger or catalytic precooler, which exhibits catalytic activity for the destruction of ozone, in combination with an ancillary or augmentative catalytic device also for the destruction of ozone, wherein the weight of the augmentative catalytic device is less than that of prior art stand-alone catalytic converters. Because the augmentative catalytic device may be smaller in size than a stand-alone catalytic converter, any pressure drop within the system may be mitigated.
There is also a need for a catalytic heat exchanger system having a catalytic precooler in series with an augmentative catalytic device, wherein each of the catalytic precooler and the augmentative catalytic device are adapted for ozone removal from an air stream, and wherein the total weight of the catalytic heat exchanger system is less than the combined weight of a non-catalytic precooler and a stand-alone catalytic converter of the prior art.
There is a further need for a catalytic heat exchanger system having a catalytic precooler in series with an augmentative catalytic device, wherein the overall ozone conversion efficiency of the catalytic heat exchanger system is at least about 85% after 30,000 hours of operation, and wherein the direct maintenance cost for the catalytic heat exchanger and ancillary catalytic device is less than that of prior art stand-alone catalytic converters.